Look. No where in the original posting did she say all men do anything. The original title was "males" not "all males" and in the text she just lists the things she doesn't want men to do. If you don't do those things, then everyone should be happy. If you do do those things, then yes the letter is relevant to you.
But I can improve the analogy, if you like. Let's make it a unisex toilet, in a coffee shop I guess. Same sign. Now women could be squatting in a public sink rather than waiting for a cubicle to become free, but that's pretty embarrassing and humiliating for most women, but there are some men that like to treat the world as their urinal, and men could use the sink without disrobing, so I would guess that if someone was urinating in the sink, it was going to be men. Would you complain about that sign? Or believe it somehow gave women permission to piss in the sink?